Some internal combustion engines include a crankshaft rotatably supported on a cylinder block, a crank timing sprocket positioned on the crankshaft, and a camshaft rotatably carried on a cylinder head for opening and closing intake and exhaust valves, which cylinder head is disposed on the cylinder block. Also included is a cam sprocket positioned on the camshaft, a timing chain wrapped around the crank timing sprocket and the cam sprocket, an enclosing member extending over the cylinder block and the cylinder head so as to cover the timing chain to form a chain chamber, and an oil pump disposed on the crankshaft on the side of the cylinder block.
In recent years, in some internal combustion engines, a variable valve timing system is provided for varying the valve timing of intake and exhaust valves in order to enhance a variety of required functions.
As illustrated in FIG. 11, the variable valve timing system is provided with: an oil pump 204 and a crank shaft timing sprocket 206, both disposed on a crankshaft 202; intake and exhaust camshaft sprockets 212, 214 disposed on intake and exhaust camshafts 208, 210, respectively; a timing chain 216 wound around the crankshaft timing sprocket 206 and the camshaft sprockets 212, 214; a hydraulic actuator 218 provided as hydraulic equipment at an end portion of the intake camshaft 208; an oil control valve 220 positioned in a cylinder head (not shown) for actuating the hydraulic actuator 218; and, control means such as an electronic control unit (ECU) 222 (shown schematically) for actuating the oil control valve 220. The control means 222 communicates with a crank angle sensor 224 and a cam angle sensor 226 via electrical signals (shown in dotted lines in FIG. 11) to calculate optimum valve timing in accordance with a running state of an internal combustion engine (not shown). The control means 222 actuates (via an electrical signal) the oil control valve 220 so as to control hydraulic pressure on the hydraulic actuator 218, thereby varying respective phases of the intake camshaft 208 and the crankshaft 202.
As illustrated in FIG. 12, in order to introduce oil from the oil pump 204 on the cylinder block side to the oil control valve 220 on the cylinder head side, an oil pipe 228 is mounted in the following manner: a pipe connection member 230 at one end of the oil pipe 228 is mounted on a cylinder block 234 by means of a union bolt 232; and a pipe connection member 236 at the other end of the oil pipe 228 is mounted on an intake camshaft cap 240 by means of an additional union bolt 238. The intake camshaft cap 240 retains the intake camshaft 208. The oil pipe 228 is exposed and laid outside the engine.
Examples of such an oil passageway structure are disclosed in, for example, published Japanese Utility Model Application Laid-Open No. 5-6112, Japanese Patent Application Laid-open No. 8-232625, Japanese Patent Application Laid-Open No. 8-28231, Japanese Patent Application Laid-Open No. 9-170415, and Japanese Utility Model Application Laid-Open No. 62-179314. According to Japanese Utility Model Application No. 5-6112, a chain cover, i.e., an enclosing member, is formed with an oil passage in an internal combustion engine which has the oil pump positioned at a lower portion of the cylinder block. According to Japanese Patent Application No. 8-232625, a plurality of linear communication pipes are connected to an oil gallery in a crank case. Pursuant to Japanese Patent Application No. 8-28231, a hydraulic control valve, i.e., an oil control valve, is provided in a dead space of the cylinder block. According to Japanese Patent Application No. 9-170415, the cylinder head is formed with the oil passage in an internal combustion engine having variable valve timing. Pursuant to Japanese Utility Model Application No. 62-179314, a lubricating oil pipe is laid or disposed in the crank case.
In the past, with the internal combustion engine having the variable valve timing system, an inconvenience occurs when an oil pipe is laid outside the engine. This oil pipe extends from a main gallery as an oil passageway system which leads to the oil control valve. The main gallery is formed in the cylinder block. The inconvenience is that, if oil seeps from the oil pipe, then the oil escapes to the outside environment because the oil pipe is laid outside of the engine. Further inconveniences arise when oil passages are formed in the cylinder block and the cylinder head by drilling holes therein for the sole purpose of passage of oil. More specifically, the necessity of such dedicated holes involves dedicated fabrication facilities as well as a dedicated cylinder block and a dedicated cylinder head. In addition, such dedicated holes result in a reduced amount of freedom in design. Further, since the cylinder block is fabricated by dedicated machines, fabrication lines must be modified when the quantity of dedicated holes is to be increased or changes to the holes are desired. As a result, plant investment is increased.